<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        a {

            display: inline-block;
            padding: 10px;
            border: 1px solid blue;
        }
        .on {
            background-color: blue;
            color: white;
        }

    </style>
    <script src="jQuery/jquery-1.11.3.js"></script>
    <script>
        $(function(){
            $("a").on('mouseover',function(){
                $("a").removeClass('on');               //移除所有on
                $(this).addClass('on');      //this当前的html元素对象  $(this) 将html对象转换成 jQuery对象   //显示当前on

            })
        });
    </script>
</head>
<body>
<a href="#" >1</a>
<a href="#">2</a>
<a href="#">3</a>
<a href="#">4</a>
<a href="#">5</a>
</body>
</html>